Project Summary Mitochondria adapt their shape and influence cellular metabolism in response to the physiological state of the cell. Cristae are dynamic compartments of the mitochondrion that dictate its bioenergetic capacity by regulating the kinetics of Oxidative Phosphorylation (OXPHOS) reactions and the structure of the OXPHOS complexes. Cristae shape is regulated during many pathological conditions, including mitochondrial diseases with no available cure. Here, the molecular mechanisms that underlie cristae remodeling will be investigated to rescue bioenergetic defects observed in mitochondrial disorders by combining ultrastructural, biochemical and bioenergetic analyses. The Puigserver Lab has shown that a component of the ER stress response, R(PKR)-like ER kinase (PERK), remodels cristae and mediates an energetic shift to promote mitochondrial respiration through the elf2?-ATF4 axis. The communication between the ER and mitochondria in the context of cristae formation is a relatively under-explored area and the regulation of this cross-talk is unclear. This proposal investigates a novel role for the PERK pathway in rescuing cristae shape during mitochondrial disease. Aim 1 focuses on the downstream effects of PERK and how the metabolomic and proteomic signatures of mitochondria are altered to rescue bioenergetic defects seen in OXPHOS Complex I deficient cells. Aim 2 characterizes the contribution of the ER-mitochondria contact sites to PERK mediated cristae formation. Aim 3 explores additional kinases like PERK that are known to phosphorylate elf2? in response to different types of stress, and their potential role in rescuing bioenergetic defects in mitochondrial mutants. The Puigserver is part of a dynamic research community at the Dana Farber Cancer Institute and Harvard Medical School, with established tools, cell lines and methodologies to explore mitochondrial metabolism and perform all the proposed experiments. These studies hope to identify and explore new pathways that regulate cristae shape to rescue bioenergetic defects associated with mitochondrial disease.